This invention relates to an image display system for nuclear or gamma cameras such as are used in the practice of nuclear medicine.
One invention disclosed herein is for achieving high speed addition or subtraction of picture element (pixel) data before it is entered into a display controller memory. One purpose for which high speed image addition or subtraction is needed is to produce the visual effect, in the image display, of radioisotope-infused blood flowing into an anatomical region of interest such as the arteries or chambers of the heart. This requires subtraction or addition of image data at a very high speed to produce a flicker-free display on the screen of a television monitor.
The new high speed image addition and subtraction method and apparatus described herein is used in conjunction with a conventional nuclear camera, or scintillation camera as it is sometimes called, to sense the gamma ray photons emitted from a body in which a radioactive isotope has been administered. The camera used is similar to the well-known Anger camera described in U.S. Pat. No. 3,011,057.
One known method of adding or subtracting the digital pixel data for successive image frames involves taking the data representative of previous frames out of the display controller and then having the host central processor or computer used in the system normalize the data for the current image frame, add it to the data removed from the display controller and then restore it to the display controller for driving the TV display. Typically, a display controller memory will have 256.times.256 pixel locations. Thus, the host central processor in this prior art approach must do about 65,000 additions which typically require about 80 microseconds per addition before the data can be restored to the display controller. This results in a minimum of 5.2 seconds elapsing between presentation of successive image frames and is perceived on the display screen by the physician as a jerky and distorted image. This prior art method also has the disadvantage of loading the host central processor and the system data and address bus since the processor must perform the arithmetic operations at intervals between the other operations which it must perform. Gamma ray photon emission data coming in from the gamma camera for the present image frame may be lost in part as a result of the host computer being occupied with the arithmetic operations so it cannot properly handle incoming data during the arithmetic operation intervals.
A second prior art method accomplished frame additions at the expense of using less than the full resolution characteristics of the display controller and at the expense of performing this arithmetic operation at a non-real-time basis with the results being stored on a mass storage device such as magnetic disk. Display controllers used in nuclear camera systems can normally show a 32.times.32, 64.times.64, 128.times.128, or 256.times.256 pixel image over the full TV monitor display screen. Thus, in accordance with this prior art method, a portion of the full memory capacity is used for the image display so the remainder of the memory can be loaded with data, already added to or subtracted from the previous data by a host central processor. Since fewer pixels are added or subtracted, less time is required for the arithmetic operations and visual distortion on the display screen is reduced significantly in comparison with the prior art method first discussed above. In the second method, for example, a field of 128.times.128 pixels may be used in the display controller memory. After these pixels are loaded into the memory, a frame display switch occurs which then displays the field just loaded. Data for the reduced size field is then transferred from the display controller to the host computer for performing the pixel addition or subtraction operations after which the data is returned to the display controller for displaying the image. Even though fewer arithmetic operations are required in this prior art mode, as much as 1.3 seconds can elapse between presented images. Other disadvantages of this method are that the full resolution of the display controller cannot be used and the host computer is loaded heavily when performing frame additions or subtractions as in the previously discussed prior art method. Moreover, with either prior art method, true real-time image frame presentation cannot be achieved.
A further disadvantage of the prior art methods is that the raw image data for a preceding frame is lost when the data is removed from the display controller for making the additions or subtractions and normalizations to fill the full bit range of the display controller memory locations. For some signal processing modes it is desirable to have the raw data for the image frames available and displayed.